1. Field of the Invention
The present invention relates to a method and an apparatus for flue gas treatment that improve efficiency of treatment of carbon dioxide contained in a flue gas emitted from, for example, a gas turbine.
2. Description of the Related Art
Various techniques have been proposed to separate carbon dioxide from a flue gas generated in power plants thereby to tackle the global warming. Proposed techniques include, for example, Pressure Swing Adsorption (PSA), membrane separation, and chemical absorption. Currently, carbon dioxide separators are rarely used in gas turbine combined plants which are high-efficiency power plants. When the carbon dioxide separators are employed, however, efficiency of net power generation deteriorates significantly because carbon dioxide concentration in a flue gas emitted from such plants is relatively low and a large amount of power is required for separation (see Japanese Patent Application Laid-Open No. 2000-337108, for example).
Further, the carbon dioxide concentration in a flue gas emitted from a gas turbine is as low as 3.93%. In order to recover carbon dioxide from such facility, a large volume of flue gas must be treated, and hence a large carbon dioxide recovery apparatus must be employed.
When the flue gas emitted from the gas turbine is recycled and reused in the same gas turbine for several times, the carbon dioxide concentration can be increased. However, modification of piping systems of existing facilities is difficult. Specifically, such modification of specification is difficult to realize in the gas turbine. Thus, such techniques are not actually adopted.
As an alternative, plural gas turbines can be installed in series so that the flue gas of an upstream gas turbine is sequentially used in a downstream gas turbine. However, the specification of the gas turbine is determined scrupulously in a design phase, and there is little possibility of actual application of a simple serial installation and sequential use of plural gas turbines for the increase in carbon dioxide concentration.
As another alternative, it is possible to add a fuel to a flue gas emitted from an existing gas turbine and to re-burn in an exhaust heat recovery boiler. As shown in FIG. 12, in this case, while the carbon dioxide concentration in a flue gas 12 emitted from a gas turbine (G/T) 11 is 3.92 volume percent [vol %], the carbon dioxide concentration in a flue gas 14 from an exhaust heat recovery boiler (such as a heat recovery steam generator: HRSG) 13 can be as high as 4.6 vol %. However, it is difficult to add a large amount of fuel and re-burn. In addition, the increase is merely approximately 15%, which is insignificant. Thus, conventionally proposed techniques cannot achieve significant improvements in recovery efficiency of the carbon dioxide recovery apparatus.
In view of the foregoing, it is desirable to increase the carbon dioxide concentration in a flue gas emitted from a gas turbine in an existing gas turbine facility by a simple modification so as to improve the efficiency of carbon dioxide recovery.